initial commit

1 files changed, 61 insertions, 0 deletions

diff --git a/Pitfalls.txt b/Pitfalls.txt
new file mode 100644
index 0000000..b5faede
--- /dev/null
+++ b/Pitfalls.txt
@@ -0,0 +1,61 @@
+If something does not work as it should, please check the following list.
+It is compiled from the feedback we received so far.
+
+
+FIRMWARE:
+- If you use an ATMega or other device with internal RC oscillator, make sure
+  that you flash the fuse for the external crystal oscillator.
+- Make sure that all USB inputs (D+, D- and the interrupt) are configured as
+  inputs with no internal pullup resistor. You must write a "0" to the port
+  output bit and to the data direction bit of each input line.
+- Make sure that you have updated the defines in usbconfig.h to reflect your
+  pin assignments.
+
+
+HOST DRIVER:
+- On Linux you must be root in order to use libusb (unless you have configured
+  hotplug appropriately). The command line utility must therefore be executed
+  by root.
+- Our host software can be compiled on Windows using MinGW and libusb-win32.
+- libusb-win32 version 0.1.10.1 (others have not been tested) has a bug with
+  suspend mode. Once the PC was in suspend mode, the device is "lost".
+
+
+HARDWARE:
+- EMI: Our reference implementation is susceptible to EMI problems. We found
+  out that the chip performs a reset although the external reset pin does
+  not change level (checked with a DSO connected to reset and triggered by
+  USB reset). This may be a consequence of over-clocking (we had the AT90S2313
+  in stock and it just worked). We recommend EMI precautions in any case:
+  (1) Use the watchdog timer of the device, (2) generate an USB reset state
+  for an extended period of time after device reset (this is outside the USB
+  spec, but it works: the hub or host interprets it as disconnect). Otherwise
+  the host's and device's notion of the device-ID may get out of sync.
+- If you use the EEPROM, it is very likely that you need some kind of brownout
+  protection. A capacitor of several 100 microfarads in the supply is enough
+  to reliably cause brownout problems. See Atmel's Application Note AN180
+  for more information. Your local supplier's price table may be a better
+  selection guide for brownout protection chips, though. Newer AVRs have
+  brownout protection built-in. It can be configured with the fuse bits.
+- Operating Voltage: PowerSwitch has been designed to operate at 3.5 V in
+  order to meet the data signal voltage specification. The circuit does
+  not work reliably with 5 V levels on D+ and D-. These levels exceed the
+  common mode range of the USB I/O driver chips found in some hosts and hubs.
+  We therefore recommend that you either reduce the CPU's supply voltage or
+  add 3.6 V zener diodes to USB D+ and D- to clamp the voltage at 3.3 V.
+
+
+AVR DEVICES CONFIRMED TO WORK:
+Although the driver should work with all AVR microcontrollers which meet the
+criteria, it may be good to know that somebody has actually tried a particular
+chip. If you have built an AVR-USB project with a chip not listed here,
+please drop us a note. The following chips have been tested:
+
+  AT90S2313   works, although it is overclocked
+  ATTiny2313
+  ATTiny45
+  ATMega8
+  ATMega88
+  ATMega8535
+  ATMega32
+